1. Field of the Invention
The present invention is related to an ink composition suitable for inkjet recording, an inkjet recording method, a printed material obtained by using the inkjet recording method, a planographic printing plate obtained by using the ink composition, and a method for producing a planographic printing plate. Specifically, the invention is related to an ink composition which cures with high sensitivity upon irradiation with radiation to form a high-quality image and which has high storage stability, an inkjet recording method, a printed material obtained by using the ink composition, a planographic printing plate obtained by using the ink, and a method for producing the planographic printing plate. The present invention further relates to inkjet apparatuses are simple and create less noise.
2. Description of the Related Art
Methods for forming an image on an image recording medium such as paper based on an image data signal include electrophotographic methods, sublimation-type thermal transfer methods, melt-type thermal transfer methods, and inkjet methods. In electrophotographic methods, a process of forming an electrostatic latent image on a photoreceptor drum by charging and exposure to light is required, and the process makes the system complicated, resulting in problems of increased production cost and the like. Thermal transfer methods can be applied to inexpensive apparatuses; however, the use of ink ribbons increases the running cost and generates wastes.
Inkjet recording methods are applicable to inexpensive apparatuses, and can reduce the running cost. This is because an image is directly formed by providing ink only to image portions on the support, thereby improving the efficiency in the use of ink. Further, the ink jet recording methods generate less noise, and are excellent image forming methods.
Ink compositions curable by irradiation with radiation such as ultraviolet rays, especially inkjet inks (radiation-curable inkjet ink), are requested to have sufficiently high sensitivity and capability of forming high-quality images. When the sensitivity of such inks is heightened, the inks cure efficiently upon application of radiation, whereby a lot of benefits are provided including reduced electric power consumption, longer life of radiation generator owing to reduced load, and prevention of generation of low-molecular substances caused by insufficient curing. Further, when ink compositions (inkjet inks in particular) are used for the formation of the image areas on planographic printing plates, higher sensitivity increases the curing strength of the image areas, thus achieving higher printing durability.
Examples of conventionally-proposed ultraviolet-curing ink compositions include an ink composition using a mixture of a plurality of monomers possessing different degrees of functionality (for example, see Japanese Patent Application Laid-Open (JP-A) No. 5-214280). However, in order to maintain a curing speed with using such an ink composition, it is inevitable to use a multifunctional monomer in a large quantity and, for this reason, there is a problem in flexibility of an image after an ink therein is cured.
Planographic printing plates have been conventionally manufactured by using so-called PS plates. The PS plate has a configuration including a hydrophilic support and a lipophilic photosensitive resin layer. The planographic printing plates have been manufactured by a method including image-forming by exposing the photosensitive resin layer imagewise so as to increase or decrease the solubility of the exposed portion with respect to an alkali developer and removing a non-image portion by dissolving. In recent years, however, digital technology in which image information is processed, stored, and outputted electronically by computer is becoming more and more popular, and there is a need for a new image-output method compatible with the digital technology. Particularly, methods which enable direct production of printing plates without a treatment using a developer have been investigated, and methods of directly forming planographic printing plates by using ink compositions for inkjet recording are under development. The methods of directly forming planographic printing plates include ejecting, by an inkjet method or the like, an ink onto a surface of a support imagewise, the support preferably being hydrophilic, and irradiating activated radiation so as to cure the ink, in order to obtain a printing plate having a desired image, which is preferably a hydrophobic image. In order to form an image portion of a planographic printing plate, it is desirable to obtain the properties of rapid curing of ink droplets ejected onto a support without blurring, excellent strength of a cured image, excellent adherence of a cured image to a support, and excellent flexibility to an extent that allows for bending of a support when the planographic printing plate is applied to a printer without incurring damage such as cracks, and thus ink compositions satisfying these properties are currently sought after.
Accordingly, there has been a need for an ink composition which cures with high sensitivity upon irradiation with activated radiation, is capable of forming a high-quality image with superior adhesion to a recording medium, and preferably further has high flexibility, as well as a need for a method using such an ink composition.
There has also been a need for a planographic printing plate which is obtained by using an ink composition which cures with high sensitivity upon irradiation with activated radiation, (which is preferably ultraviolet ray,) as well as a need for a method for producing such a planographic printing plate.